Question 72 from the Impossible Quiz is the second searching question of the game (and the third in the series), where the screen is completely black and you must find one small object, which is a light switch. It's a safe question, so you're free to click wherever you want on the screen.

You must find a clickable spot among the darkness, which is where the switch is located. It's on the far left end of the screen, somewhere between the question number and the lives. Once clicked, the light on the top of the screen will be turned on, revealing a picture of a funny-faced lemur (the light is absent from the iOS version).

Question 105 from The Impossible Quiz 2 also requires you to look for a light switch in the middle of the darkness, though in that case it's located under the question number itself. The picture is different too.